The overall goal of the proposed research is to determine the previously unrecognized role of the (long non-coding RNA) lncRNA NEAT1 (nuclear paraspeckle assembly transcript 1) and its novel underlying mechanism in regulating the phenotypic switching of vascular smooth muscle cells (VSMCs). Many vascular diseases in humans, such as intimal hyperplasia post-angioplasty, are largely dependent upon VSMC phenotypic switching from a contractile to a synthetic phenotype that is associated with reduced smooth muscle-specific gene expression and increased cell proliferation and migration. Therefore, unraveling the mechanisms for the VSMC phenotypic switching is crucial for understanding the pathology of VSMC related vascular diseases and ultimately designing therapeutic agents for treatment. Emerging evidences demonstrate that lncRNAs represent a novel class of regulators for gene expression. In an effort to search for lncRNAs involved in the vascular injury, we conducted a large-scale lncRNA array screen using the rat carotid artery injured by a balloon denudation, a procedure resembling angioplasty in humans. This screen revealed that the lncRNA NEAT1 is induced in response to the arterial injury in vivo. Furthermore, expression of NEAT1 is also induced upon the stimulation of smooth muscle phenotypic modulation in vitro. Loss- and gain-of-function NEAT1 revealed that NEAT1 not only increases proliferation and migration of VSMCs but also decreases expression of smooth muscle-specific contractile proteins. Therefore, experiments described in this proposal will test the hypothesis that, the induction of NEAT1 plays a critical role in promoting smooth muscle phenotypic switching. In Aim 1, we will determine the role of NEAT1 in neointima hyperplasia following arterial injury. We will perform femoral artery wire injuries in the control and NEAT1 knock out mice and assess the effects of NEAT1 KO on the progression of neointima hyperplasia. In Aim 2, we will determine the mechanism by which NEAT1 abrogates smooth muscle-specific gene expression. Specifically we will evaluate the role of WDR5, a critical histone modifier for inducing an active form of chromatin, in mediating NEAT1 function in VSMCs. In Aim 3, we will determine the mechanism by which the transcription of NEAT1 is up-regulated upon the stimulation of smooth muscle phenotypic modulation by testing the role of an evolutionally conserved cAMP response element identified in the NEAT1 proximal promoter. Completion of these studies will provide novel insights into the mechanisms controlling smooth muscle phenotypic switching and determine if preventing the induction of NEAT1 may be an attractive therapeutic strategy for ameliorating occlusive vascular diseases.